‘YOU may have noticed, I have turned into a grumpy old man,” says James MacMillan. The Scottish composer, new knight of the realm, former Twitter lightning rod and, it emerges, recently retired controversialist, is in a good mood. When we meet, his Fourth Symphony has just premiered at the Proms to grand reviews. And the surroundings – his former school, Cumnock Academy in East Ayrshire – are comfortably familiar.

In the school’s main hall, four young musicians are studiously working on one of their songs along with musicians from the Hebrides Ensemble, as well as lyricist and academic Davie Scott, singer-songwriter Jo Mango and MacMillan himself. The band, all aged 17 and 18 and from the Kilmarnock area, are playing guitars and bass, and have been intently collaborating with the musicians all day. This workshop is part of the community element of the Cumnock Tryst, a music festival founded and directed by MacMillan. Now in its second year, it opens this Thursday, and will see a series of concerts and performances at venues in and around MacMillan’s home town.

After the music workshop, we retire to a staff room to discuss Macmillan’s recent move away from Glasgow after 25 years, his new knighthood, his controversial views on art and politics ... and his criticism of this newspaper.

MacMillan – a vocal opponent of Scottish independence – has been far from complimentary in the past. In February, he tweeted that the independence-supporting Sunday Herald was a “disgrace to journalism”. But today he is sanguine. “I speak to everybody,” he says. “I don’t have a problem at all.” He spent much of the year of the referendum and preceding years being outspoken, sometimes snarky, on Twitter, but now he is off it. His Twitter feed is currently run by his publishers.

His presence on Twitter was controversial, especially his views on the National Collective, the pro-independence group of artists and creatives. In 2013 he tweeted: “The National Collective has a creepy, fascistic mob mentality. Scottish artists of individual integrity should avoid them.” He also wrote: “I don’t understand artists who suck up to Government politicians, or those who want to huddle in ‘collectives’ like Mussolini’s cheerleaders.”

Now, MacMillan says he “tried my best to keep out of” the “indyref” debate. I raise an eyebrow. “It was only the matter of arts and politics that drew me in,” he insists. “It seemed to be channelled through the referendum, but there is a wider anxiety that I have about artists and politics and how it can work.

“Sometimes it can work very well, of course; artists have to engage with politics sometimes for their work. Otherwise we wouldn’t have [Orwell’s] Nineteen Eighty-Four. I have written political pieces myself. But there has been a danger at certain points in the 20th century when artists have been seduced by the glamour of power, and sometimes very dangerous powers, and that’s what I wanted to say. I kind of knew I would get drawn in, and I didn’t want to be involved in the referendum, but it seemed to happen because that was my concern.

“To be honest,” he continues, “the actual nitty-gritty of the Yes/No thing was beyond me. I didn’t really want to feature in it. But you end up doing that. Everything was being channelled one way, and I am glad that is over.”

MacMillan also claims he was misrepresented. “I think what happens is that, no matter what you say, with social media now, especially Twitter, everything gets squashed into a little soundbite and indeed altered. So no, I didn’t say people [The National Collective] were Mussolini’s cheerleaders, I used a simile that was lost in translation. But I realise that’s what social media does and, to be honest, that’s why I am not there any more. It’s not worth it.”

Although, he adds: “In many ways I enjoyed my time on it, it was funny. Until it got abusive and nasty, I suppose I did enjoy it. It could be harmless.”

At 56, MacMillan says he has developed “a thick skin”. “I think a lot of artists do. A lot is said about artists, because of their work, and you have to take it on board or you suffer. Young artists especially find it very difficult – I did – and maybe some are in that position right now. And with some it gets personal, your mental health is doubted and so on, but even then you realise it’s part of a bigger background context. Most of the time it is not me they hate, most of the time they do not even know me.”

MacMillan says he is now withdrawing from commenting overtly on Scotland’s politics. He insists he has “decided not to say anything more. I am still a political animal and I am intrigued by it all. But I am leaving that behind. I have got so much to look after – I want this festival to thrive, and it does not need me being Public Enemy Number One or Mr Controversial."

Inspired by the St Magnus Festival in Orkney (founded by Sir Peter Maxwell Davies and George Mackay Brown) and the Aldeburgh Festival of Music and the Arts (founded by Benjamin Britten), the Cumnock Tryst was created by MacMillan with the aim of bringing world-class musicians to the area of Scotland where he grew up. To that end he has already succeeded, as the renowned King's Singers will perform here on Friday.

Nicola Benedetti, another classical superstar from Ayrshire, is a patron of the festival, and though she's not playing this year, two other BBC Young Musician of the Year winners will: pianist Martin James Bartlett and cellist Laura van der Heijden. Jay Capperauld, from New Cumnock and a graduate composer from the Royal Conservatoire of Scotland in Glasgow, is to unveil a new commission.

After the festival opens on Thursday with a concert by the Whitburn Band, the young musicians currently rehearsing in the school hall – Gregor Lamour, Nathan Lennox, Bryce Campbell and Mathew McAteer – will perform on Friday at Cumnock Academy. There will also be a collaboration between the festival and Drake Music Scotland, including children from Hillside School and Barshare Primary School. On Saturday, the newly founded Festival Chorus will make its debut with Faure's Requiem.

MacMillan does not want the festival to be “stale”. He already has some ideas about bigger venues. Folk and brass music are being included, and more experimental forms will be included in the future. The composer positively glows while talking about the Cumnock Tryst's potential.

“We have high-calibre performers, and that will continue," he says. "I have some very interesting people coming in future years. It is very exciting that they are all saying yes. But we also want the local people here to feel complete ownership of it. It is not an area that gets a lot of arts provision. Cumnock is an area of multiple deprivation. It was all mining and farming when I grew up here, but I remember it as having a lot of people interested in music, whether it was brass bands, choirs or whatever. We are developing what’s here, allowing them to grow and blossom.”

MacMillan, who lived in Cumnock until 1977 and attended the Academy for four years, has designed the festival to work with schools in Cumnock, Kilmarnock and Dalmellington. These workshops can inspire as well as instruct, he believes. “There is no wrong answer. They can try out whatever they like. You can see their excitement.”

However, the composer remembers an earlier, pre-school experience of his own, at the age of five, that was more of a personal epiphany, melding together two key influences in his life: music and Roman Catholicism.

“I was taken to St Mary’s Metropolitan Cathedral in Edinburgh when my parents were on holiday. I do remember this wonderful music in St Mary’s. I remember this incredible sound world, and it was associated with what was going on, of course, the rituals, but it just seemed magical and delightful. I always remember the feeling of mystery but also the joy of what I was encountering.”

Today, he looks around his old school's small staff office. “It hasn't changed much," he notes. "This was the staff room, then and now. That hallway has the same smell about it that I remember.”

How was his time at school? “It was good. There was lots of music. I sang in the choir then. The head of music, Bert Richardson, got us all involved singing music that probably wouldn't have been sung here before, lots of Palestrina and Bach, and I fell in love with it ... And lots of people in the choir fell in love with each other. The strange thing is that many couples came out of that choir, including me and my wife Lynne. Also my wife’s brother and his wife, friends, all married each other – because of something that was happening here in the late 1970s.”

MacMillan and his wife, who have been together since 1976 ("the Medieval times", he jokes), have three children: Catherine and twins Aidan and Clare. Now, after 25 years living in Glasgow, the couple are moving out of the city to the north Ayrshire countryside, near Largs. The solitude and peace of the rural life was one attraction for the composer. And now that his children have left home, he felt a change was due. The new house is quieter and overlooks Cumbrae and Arran.

“It’s a wrench," he admits. "I love Glasgow and brought up our children there. But as a composer I spend a lot of time on my own, as composers need to do. We are not too far from the [Glasgow International] airport, which is a big consideration, because when I am not working at home I am off conducting.

“I am hoping it will be advantageous for me. When I say a ‘grumpy old man’, I mean it is noise that is affecting me. Obviously I have lived in a noisy house with three children, but now it is things like car alarms, house alarms, workmen playing their transistor radios outside – that's a whole day ruined if that happens.”

Will the new environment affect his music? “I am not sure. I have certainly found it advantageous to be in the countryside writing, whether on holiday or on retreat at Pluscarden Abbey [near Elgin]. There is a settling of the mind and the soul in these places.”

The Tryst, and MacMillan’s long-term plans for it, are a kind of homecoming for the composer, but he has always felt connected to the town and its area. “I never really left, in the sense that I still had family here,” he says. His mother, Ellen, died six years ago, but his father, also James, lived here until recently. So where did his musical talent come from? His mother studied music in school, and played piano well. His father plays the piano by ear. MacMillan’s maternal grandfather, George Loy, a coal miner, was a euphonium player who loved music and wanted his daughter to be a musician. He was the man who took young James to his first band practices, gave him his first organ tutor books, and he loved what his grandson was doing. He died 20 years ago, and MacMillan has Loy as a middle name.

And now he has an honorific at the beginning of his name. MacMillan was given a knighthood in the Queen’s Birthday Honours earlier this year. He said he never had any doubt about accepting it, but is still deciding whether to be knighted at Holyrood Palace or at Buckingham Palace. “It came as a complete surprise. I just remember going very hot and red all over, and I was astonished, but delighted, and very honoured. I see it obviously as a personal honour but also as an honour for music, and modern music in particular.”

Just before he is called away, when we are talking again about politics and art, MacMillan mentions he has been thinking about other composers and their relationship to society.

“Controversy and societal change have affected many composers," he says. "I have been thinking a lot about Beethoven, and how he eventually rejected the glamour of the tyrants, how he rejected Napoleon and the revolutionary violence he stood for, by tearing off the dedication page of the Eroica Symphony. Artists need to look to the likes of Beethoven, rather than Hugh MacDiarmid, I would say. Shostakovich made a decision to stay schtum [in Soviet Russia]. He is an interesting example of someone who said everything through his music.”

And, it seems, that is how James MacMillan will now express his opinions – through a score, and no longer online.

The Cumnock Tryst takes place from October 1-4. For full programme details, see www.thecumnocktryst.com